Cast material and method of manufacturing cast material

ABSTRACT

A cast material comprising hard phase particles mainly composed of a boride and/or a carbide, and a binder phase including an alloy mainly composed of Co and/or Ni. The average particle size of the hard phase particles is 3 μm or less, the average value of the aspect ratios of the hard phase particles is 2.3 or less, the content of the hard phase particles having a major axis exceeding 5 μm is 3 particles or less per 2,450 μm 2 , and the contact ratio between the hard phase particles is 40% or less.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a cast material and a method ofmanufacturing a cast material.

Brief Description of the Related Art

Requirements for wear resistant materials used in various mechanicalfacilities and mechanical devices have come to be increasingly severeyear by year; recently, wear resistant materials have been demanded tobe not only high in wear resistance but also excellent in corrosionresistance, heat resistance and the like.

As such wear resistant materials, cermet materials, namely, compositematerials between ceramics and metals have hitherto been investigated.As the methods of manufacturing such cermet materials, there has beenknown a method in which, for example, by a powder metallurgy method,powders to be raw materials are mixed with each other, and subjected tofiring at a temperature equal to or lower than the melting points of theraw materials, in a state of being molded by mold pressing or the like.

When the powder metallurgy method is used, because the raw materials arenot melted, excessive grain growth in raw materials can be suppressed,and the generation of shrinkage cavities or dendrite microstructures(columnar crystals) can be prevented. On the other hand, when the powdermetallurgy method is used, because voids remain in the interior of theobtained cermet material, the density of the obtained cermet materialsometimes comes to be insufficient.

In contrast, Patent Document 1 discloses a method for obtaining a castmaterial including Mo (molybdenum), Ni (nickel), B (boron) and the like,by using cast method.

PRIOR ART DOCUMENT

[Patent Document]

[Patent Document 1] WO 2012/063879

SUMMARY OF THE INVENTION Problems to be Solved by Invention

However, a cast cermet material obtained by the cast method described inforegoing Patent Document 1 is improved in density, and additionally,dendrite microstructure tend to grow in the interior of the cast cermetmaterial. Accordingly, the cast material obtained by the cast methoddescribed in Patent Document 1 is liable to be broken due to the growndendrite microstructures to function as breakage origins. Therefore, ithas been difficult to use the cast material obtained by the cast methoddescribed in Patent Document 1, in particular, in applications requiringbending strength.

An object of the present invention is to provide a cast material beingexcellent in corrosion resistance and wear resistance, and achieving ahigh hardness and a high bending strength.

Means for Solving Problems

The present inventors have perfected the present invention bydiscovering that the foregoing object can be achieved by controlling theaverage particle size of hard phase particles, the average value of theaspect ratios of the hard phase particles, the content of the hard phaseparticles having a major axis exceeding 5 μm, and the contact ratiobetween the hard phase particles so as to fall within specific ranges,in a cast material comprising the hard phase particles mainly composedof a boride or a carbide and a binder phase including an alloy mainlycomposed of Co and/or Ni.

That is, according to an aspect of the present invention, there isprovided a cast material comprising hard phase particles mainly composedof a boride and/or a carbide and a binder phase including an alloymainly composed of Co and/or Ni, wherein the average particle size ofthe hard phase particles is 3 μm or less, the average value of theaspect ratios of the hard phase particles is 2.3 or less, the content ofthe hard phase particles having a major axis exceeding 5 μm is 3particles or less per 2,450 μm², and the contact ratio between the hardphase particles is 40% or less.

In the cast material according to the present invention, the hard phaseparticles are preferably particles of the boride and/or the carbidecomposed of at least one of Ni, Co, Cr, Mo, Mn, Cu, W, Fe and Si, and Band/or C.

In the cast material according to the present invention, the binderphase is preferably the alloy composed of at least one metal of Cr, Mo,Mn, Cu, W, Fe and Si, and Co and/or Ni.

In the cast material according to the present invention, the content ofB in the cast material is preferably 1 to 6 wt %, and the content of Cin the cast material is 0 to 2.5 wt %.

In the cast material according to the present invention, the hard phaseparticles are preferably composed of a composite boride represented byMo₂NiB₂ or Mo₂(Ni,Cr)B₂, and the binder phase is preferably composed ofa Ni-based alloy.

Moreover, according to another aspect of the present invention, there isprovided a method of manufacturing a cast material comprising the hardphase particles mainly composed of a boride and/or a carbide, and abinder phase including an alloy mainly composed of Co and/or Ni, whereinthe production method includes a step of obtaining a fused mixture bydissolving the raw materials for forming the cast material in a state ofbeing mixed with each other, and a step of cooling the fused mixture,the step of cooling the fused mixture including a process ofcontinuously cooling the fused mixture, at a cooling rate of 100° C./minor more, in a temperature range from the cooling starting temperature to400° C.

It is preferred in the manufacturing method according to the presentinvention to perform the cooling of the fused mixture by pouring thefused mixture into a mold set at room temperature to 1100° C.

Effect of Invention

According to the present invention, there can be provided a castmaterial excellent in corrosion resistance and wear resistance, andachieving a high hardness and a high bending strength.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram for illustrating the measurement method of themicrostructure of the cast material according to the present invention.

FIG. 2A and FIG. 2B are photographs showing a backscattered electronimage of a cross section of the cast material of Example 1 taken byusing a scanning electron microscope (SEM).

FIG. 3A and FIG. 3B are photographs showing a backscattered electronimage of a cross section of the cast material of Example 2 taken byusing a scanning electron microscope (SEM).

FIG. 4A and FIG. 4B are photographs showing a backscattered electronimage of a cross section of the cast material of Example 3 taken byusing a scanning electron microscope (SEM).

FIG. 5A and FIG. 5B are photographs showing a backscattered electronimage of a cross section of the cast material of Example 4 taken byusing a scanning electron microscope (SEM).

FIG. 6A and FIG. 6B are photographs showing a backscattered electronimage of a cross section of the cast material of Example 5 taken byusing a scanning electron microscope (SEM).

FIG. 7A and FIG. 7B are photographs showing a backscattered electronimage of a cross section of the cast material of Comparative Example 1taken by using a scanning electron microscope (SEM).

FIG. 8A and FIG. 8B are photographs showing a backscattered electronimage of a cross section of the cast material of Comparative Example 2taken by using a scanning electron microscope (SEM).

FIG. 9A and FIG. 9B are photographs showing a backscattered electronimage of a cross section of the cast material of Comparative Example 3taken by using a scanning electron microscope (SEM).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the cast material according to the present invention willbe described.

The cast material according to the present invention comprises hardphase particles mainly composed of a boride or a carbide and a binderphase including an alloy mainly composed of Co and/or Ni, wherein theaverage particle size of the hard phase particles is 3 μm or less, theaverage value of the aspect ratios of the hard phase particles is 2.3 orless, the content of the hard phase particles having a major axisexceeding 5 μm is 3 particles or less per 2,450 μm², and the contactratio between the hard phase particles is 40% or less.

<Hard Phase Particles>

The hard phase particles constituting the cast material according to thepresent invention mainly comprise a boride and/or a carbide, andcontributes to the hardness and the wear resistance of the castmaterial. In the cast material according to the present invention, thehard phase particles are present in a state of being dispersed in thematrix of the binder phase to be described later.

Examples of the boride and the carbide constituting the hard phaseparticles may include, but are not particularly limited to, precipitatedparticles comprising at least one of Ni, Co, Cr, Mo, Mn, Cu, W, Fe andSi, and B and/or C. The hard phase particles may be particles in whichparticles different from each other in composition are mixed.

Examples of the boride may include, but are not particularly limited to,MB-type, MB₂-type, M₂B-type, M₂B₅-type, and M₂M′B₂-type borides (M andM′ each represent at least one metal of Ni, Co, Cr, Mo, Mn, Cu, W, Feand Si, and M′ represents a metal element different from M); specificexamples of the boride may include borides such as CrB, MoB, Cr₂B, Mo₂B,Mo₂B₅, Mo₂FeB₂, Mo₂CrB₂, and Mo₂NiB₂.

Examples of the carbide may include, but are not limited to, M₂₃C₆-type,M₄C-type, M₃C₂-type, M₂C-type, and MC-type carbides (M represents atleast one metal of Ni, Co, Cr, Mo, Mn, Cu, W, Fe and Si, and M may besubstituted with a different metal element(s)); specific examples of thecarbide may include carbides such as Cr₂₃C₆, Cr₃C₂, Cr₆C, Mo₂C, and CrC.

The content ratio of the above-described hard phase particles in thecast material according to the present invention is preferably 10 to 50vol %, and further preferably 20 to 45 vol %. As a method forcontrolling the content ratio of the hard phase particles in the castmaterial, there can be used a method in which the content of B containedin the cast material or the content of C contained in the cast materialis adjusted. By setting the content ratio of the hard phase particleswithin the above range, it is possible to make the cast materialaccording to the present invention be highly balanced among thecorrosion resistance, the wear resistance, and the mechanical strengthssuch as the hardness and the bending strength. Moreover, by setting thecontent ratio of the hard phase particles within the above range, it ispossible to prevent the contact ratio between the hard phase particlesfrom being too large, and the bending strength of the cast material frombeing decreased due to the aggregation of the hard phase particles. Bysetting the content ratio of the hard phase particles within the aboverange, the temperature required for melting the raw materials of thehard phase particles can be lowered, and thus the energy required formelting is suppressed to lead to an advantage in cost.

<Binder Phase>

The binder phase constituting the cast material according to the presentinvention comprises an alloy containing Co and/or Ni as a maincomponent(s), and is a phase for forming a matrix for binding theabove-described hard phase particles. Specific examples of the alloyconstituting the binder phase include Co-based alloys and/or Ni-basedalloys containing at least one of Cr, Mo, Mn, Cu, W, Fe and Si. In thecast material according to the present invention, by allowing the binderphase to include an alloy mainly composed of Co and/or Ni, the corrosionresistance of the obtained cast material is improved as compared withthe case where the binder phase includes an alloy mainly composed of aFe-based alloy.

As the hard phase particles and the binder phase constituting the castmaterial according to the present invention, among the above-describedconstitutions, preferred is a constitution in which in particular, thehard phase particles comprise a composite boride represented by Mo₂NiB₂,and the binder phase comprises a Ni-based alloy.

<Microstructure of Cast Material>

In the cast material according to the present invention, themicrostructures thereof, specifically, the average particle size of thehard phase particles, the average value of the aspect ratios of the hardphase particles, the content of the hard phase particles having a majoraxis exceeding 5 μm, and the contact ratio between the hard phaseparticles are controlled within the specific ranges to be describedlater. According to the present invention, by controlling thesequantities within the specific ranges to be described later, the castmaterial can be excellent in corrosion resistance and wear resistance,and can be provided with a high hardness and a high bending strength.

In the cast material according to the present invention, the averageparticle size of the above-described hard phase particles is 3 μm orless, preferably 2.8 μm or less, and further preferably 2.5 μm or less.By setting the average particle size of the hard phase particles withinthe above range, the hardness and the bending strength of the obtainedcast material can be made sufficient. When the average particle size ofthe hard phase particles exceeds 3 μm, there occurs a failure that thehard phase particles function as origins, and the bending strength ofthe cast material is remarkably lowered. The lower limit of the averageparticle size of the hard phase particles is not particularly limited,but is preferably 0.5 μm. In order to make the average particle size ofthe hard phase particles less than 0.5 μm, the cooling rate is requiredto be extremely large, such a large cooling rate is hardly achieved byusual water cooling or the like; an achievement of such a large coolingrate leads to a production cost increase.

The average particle size of the hard phase particles can be measured,for example, by calculating the equivalent circle diameters of the hardphase particles, and by calculating the average value of the calculatedequivalent circle diameters. Specifically, first, by using a scanningelectron microscope (SEM), a backscattered electron image of a crosssection of the cast material is taken, and by using the obtainedbackscattered electron image, the average particle size of the hardphase particles can be calculated on the basis of the formula of Fullman(the following formula (1)).

d _(m)=(4/π)×(N _(L) /N _(S))  (1)

In the above-described formula (1), d_(m) represents the averageparticle size of the hard phase particles; n represents the ratio of thecircumference of a circle to its diameter; N_(L)represents the number ofthe hard phase particles per unit length of an arbitrary straight-linesegment hit by the arbitrary straight-line segment (when an arbitrarystraight-line segment is drawn, brought into contact with or intersectwith the arbitrary straight-line segment) on a cross sectionalmicrostructure; specifically, N_(L) is the value calculated by dividing,by the length L of the arbitrary straight-line segment, the number ofthe particles hit by the arbitrary straight-line segment having thelength of L on a cross sectional microstructure; and N_(S) representsthe number of the hard phase particles included in an arbitrary unitarea, namely, the value obtained by dividing the number of the particlesincluded in an arbitrary measurement area having a measurement regionrange S by the arbitrary measurement region range S. In this case, thelength of the straight-line segment L can be a length intersecting asufficient number of the hard phase particles for the measurement of theaverage particle size, and is preferably set to be 20 μm or more. InExamples to be described later, the length of the straight-line segmentL is set to be 42 μm. The measurement region range S can be a rangeincluding a sufficient number of the hard phase particles for themeasurement of the average particle size, and is preferably a rangehaving a length of 20 μm or more and a width of 20 μm or more. InExamples to be described later, the length and the width of themeasurement region range S are 57 μm and 43 μm, respectively (namely,the area is 2,450 μm²).

In the cast material according to the present invention, the averagevalue of the aspect ratios of the hard phase particles, namely, theaverage value of the ratio (major axis/minor axis) of the major axis tothe minor axis is 2.3 or less, preferably 2.2 or less and furtherpreferably 2.1 or less. By setting the average value of the aspectratios of the hard phase particles within the above range, the bendingstrength of the cast material can be remarkably improved. When theaverage value of the aspect ratios of the hard phase particles is toolarge due to, for example, the growth of the dendrite microstructures(columnar crystals), in the dendrite microstructure portion, the bendingstrength of the cast material is lowered and the cast material tends tobe broken.

The average value of the aspect ratios of the hard phase particles canbe determined according to JIS R1670, as follows. First, a cast materialis cut, and the cut cross section is photographed by using a scanningelectron microscope (SEM) to obtain a backscattered electron image.Next, from the obtained backscattered electron image, in the same manneras in the above-described measurement of the average particle size, apredetermined number of the hard phase particles are selected from theabove-described measurement region range S (a range of a length of 20 μmor more and a width of 20 μm or more), and the length (major axis) ofthe longest portion and the length (minor axis) of the longest portionin the direction perpendicular to the major axis of each of the hardphase particles are measured. Then, from the measured major axis andminor axis, the ratio (major axis/minor axis) of the major axis to theminor axis can be determined as the aspect ratio of the hard phaseparticle. In the present invention, for a predetermined number (forexample, 10 or more) of the hard phase particles, such aspect ratios aredetermined and the average value of the aspect ratios is calculated, andthus the average value of the aspect ratios of the hard phase particlescan be determined.

In the cast material according to the present invention, the content ofthe hard phase particles having a major axis exceeding 5 μm is 3particles or less, preferably 2 particles or less and further preferably1 particle or less, per 2,450 μm². By setting the content of the hardphase particles having a major axis exceeding 5 μm within the aboverange in the cast material, the bending strength of the cast material aswell as the control of the average value of the aspect ratios of thehard phase particles can be remarkably improved. The number of the hardphase particles having a major axis exceeding 5 μm can be determined bycounting the number of the hard phase particles having a major axisexceeding 5 μm in the measurement region range S (the range having alength of 20 μm or more and a width of 20 μm or more) in abackscattering electron image taken with a SEM in an arbitrary crosssection, in the same manner as in above-described the measurement of theaspect ratios of the hard phase particles. In the present invention, inExamples to be described later, the content of the hard phase particleshaving a major axis exceeding 5 μm on the basis of the number ofparticles in the measurement region range S of 2,450 μm² for performingactual measurement; however, actual measurements are not particularlylimited to such an area range; when measurements are performed by usingthe backscattered electron images in different area ranges, theaforementioned content of the hard phase particles can be determined bya proportional calculation. For example, in the present invention, thecontent of the hard phase particles having a major axis exceeding 5 μmper an area range of 5,000 μm² can be controlled, and in this case, thecontent of the hard phase particles having a major axis exceeding 5 μmper 5,000 μm² is 6 particles or less, preferably 4 particles or less andmore preferably 2 particles or less.

Moreover, in the cast material according to the present invention, thecontact ratio (contiguity) between the hard phase particles is 40% orless, preferably 39% or less and further preferably 38% or less. Thecontact ratio between the hard phase particles is an index indicatingthe dispersibility of the hard phase particles; the lower the contactratio, the more excellent in the dispersibility the hard phaseparticles, and accordingly, the improvement of the strength is possible.When the contact ratio between the hard phase particles is too high, thecontact between the hard phase particles causes the generation of coarseaggregates, or the occurrence of grain growth due to the mutual bondingof the hard phase particles; thus, there occurs a failure that the graingrowth generation portion functions as the origin to lower the bendingstrength of the cast material.

The contact ratio between the hard phase particles can be measured, forexample, as follows. Specifically, first, by using a scanning electronmicroscope (SEM), the backscattered electron image of the surface of thecast material is photographed, a straight-line segment L for measurementhaving a predetermined length is arbitrarily drawn on the backscatteredelectron image, as shown in FIG. 1, in the same manner as in theabove-described measurement of the average particle size, and the hardphase interface present on the straight-line segment L is observed. FIG.1 is a diagram for illustrating the measurement method of themicrostructure of the cast material according to the present invention.Specifically, the hard phase particle interfaces are observed, theinterfaces on which the hard phase particles are brought into mutualcontact is designated as the hard phase-hard phase interfaces I_(HH),the interfaces on which the hard phase particles and the binder phaseare brought into mutual contact are designated as the hard phase-binderphase interfaces I_(HB), and the numbers of these interfaces arecounted. Then, in the present invention, from the number N(I_(HH)) perunit length of L1 of the hard phase-hard phase interfaces I_(HH) and thenumber N(I_(HB)) per unit length of L1 of the hard phase-binder phaseinterfaces I_(HB), the contact ratio Cont (in units of %) between thehard phase particles can be calculated on the basis of the followingformula (2):

Cont=2N(I _(HH))/[2N(I _(HH))+N(I _(HB))]×100  (2)

When the contact ratio between the hard phase particles is calculatedaccording to the above-described method, it is preferred to calculatethe contact ratio between the hard phase particles by performing thefollowing set of operations six times and by averaging the results ofthe six measurements in total: in a set of operations, the straight-linesegment L for measurement other than the above-described straight-linesegment is drawn on the SEM photograph so as to pass through the routeother than the above-described route, and the number of the hardphase-hard phase interfaces I_(HH) and the number of the hardphase-binder phase interfaces I_(HB) are counted in the same manner asdescribed above.

In the present invention, the method allowing the following quantitiesto fall within the above ranges is not particularly limited, but thefollowing method may be quoted: the aforementioned quantities are theaverage particle size of the hard phase particles, the average value ofthe aspect ratios of the hard phase particles, the content of the hardphase particles having a major axis exceeding 5 μm, and the contactratio between the hard phase particles. Specifically, there is quoted amethod in which when the cast material is manufactured, first, a fusedmixture is obtained by melting the raw materials for forming the hardphase particles and the binder phase; and next when the obtained fusedmixture is cooled, there is included a process of continuously coolingat a cooling rate of 100° C./min or more, in the temperature range fromthe cooling starting temperature to 400° C.

It is to be noted that the contact ratio between the hard phaseparticles can also be controlled by, for example, adjusting thecomposition of the cast material so as to fall within a specific range.

<Composition of Cast Material>

The composition of the cast material according to the present inventionis not particularly limited, but preferably comprises, when the binderphase includes a Ni-based alloy mainly composed of Ni, 1 to 6 wt % of B,0 to 2.5 wt % of C, 0 to 30 wt % of Co, 0 to 5 wt % of Si, 0 to 20 wt %of Cr, 5 to 40 wt % of Mo, 0 to 25 wt % of Fe, and the balance of Ni.Alternatively, when the binder phase includes a Co-based alloy mainlycomposed of Co, the composition of the cast material according to thepresent invention preferably comprises 1 to 6 wt % of B, 0 to 2.5 wt %of C, 0 to 5 wt % of Ni: 0 to 5 wt % of Si, 0 to 25 wt % of Cr, 5 to 40wt % of Mo, 0 to 25 wt % of Fe, and the balance of Co.

B (boron) is an element for forming a boride to produce hard phaseparticles. By setting the content ratio of B within the above range, thecontent ratio of the hard phase particles in the cast material can beappropriate, and accordingly, the wear resistance of the cast materialis improved. By setting the content ratio of B within the above range,the contact ratio between the hard phase particles can also be withinthe above range, and the hardness and the bending strength of the castmaterial can be improved. The content of B in the cast material ispreferably 1 to 6 wt %, and more preferably 2 to 5 wt %, either in thecast material in which the binder phase is mainly composed of Ni or inthe cast material in which the binder phase is mainly composed of Co.

By including C (carbon) in a large amount, it is possible to form acarbide to produce hard phase particles. The formation of the carbideimproves the wear resistance. On the other hand, by setting the contentratio of C within the above range, the content ratio of the hard phaseparticles in the cast material is made appropriate, and accordingly, thecontact ratio between the hard phase particles can be made to fallwithin the above range, and the hardness and the bending strength of thecast material can be improved. The content of C in the cast material ispreferably 0.15 wt % to 2.5 wt %, and more preferably 0.2 to 1 wt %,either in the cast material in which the binder phase is mainly composedof Ni or in the cast material in which the binder phase is mainlycomposed of Co. When carbon is included as an inevitable impuritywithout forming any carbide, the content of C is preferably, forexample, 0.06 wt % or less.

Ni (nickel) is, when a Ni-based alloy is used as the binder phase of thecast material, an element capable of forming the hard phase particles,and at the same time, an element capable of constituting the binderphase, and has a function to improve the corrosion resistance of thecast material. Ni has, when a Co-based alloy is used as the binder phaseof the cast material, a function to improve the corrosion resistance ofthe cast material.

Co (cobalt) is, when a Ni-based alloy is used as the binder phase of thecast material, an element capable of forming the hard phase particles,and at the same time, an element capable of constituting the binderphase, and has a function to improve the corrosion resistance of thecast material.

Si (silicon) is an element capable of constituting the binder phase ofthe cast material, and has a function to lower the melting temperaturesof the raw materials for forming the cast material. By controlling thecontent ratio of Si so as to be appropriate, the above-described meltingtemperature can be lowered, and additionally, the lowering of thebending strength of the cast material due to the increase of thecontents of the silicides in the cast material can be suppressed.

Cr is an element capable of forming the hard phase particles, and at thesame time, an element capable of constituting the binder phase, and hasa function to improve the corrosion resistance, wear resistance, hightemperature properties, hardness and bending strength of the castmaterial. By controlling the content ratio of Cr so as to beappropriate, the content ratio of the hard phase particles in the castmaterial is within the above range, and the bending strength of the castmaterial can be improved.

Mo (molybdenum) is an element capable of forming hard phase particles,and at the same time, an element capable of forming the binder phase,and has a function to improve the corrosion resistance of the castmaterial. In particular, a fraction of Mo is solid-dissolved in thebinder phase, and accordingly has a function to improve the corrosionresistance of the cast material. By controlling the content ratio of Moso as to be appropriate, the wear resistance and the corrosionresistance of the cast material can be improved.

<Method of Manufacturing Cast Material>

Next, a method of manufacturing the cast material according to thepresent invention will be described.

First, a raw material powder for forming the cast material according tothe present invention is prepared. The raw material powder can beprepared in such a way that the content ratios of the respectiveelements forming the cast material are the desired composition ratios.In the present invention, the hard phase particles mainly composed of aboride and/or a carbide may be preliminarily included in the rawmaterial powder; or alternatively, the hard phase particles are notincluded in the raw material powder, but in the process of preparing thecast material by using the raw material powder, the hard phase particlesmainly composed of a boride and/or a carbide as originating from boronand carbon contained in the raw material powder may be formed in thecast material.

Next, in order to pulverize, if necessary, the prepared raw materialpowder to a predetermined particle size, a binder, an organic solventand the like are added to the raw material powder, and these are mixedand crushed by using a crusher such as a ball mill.

The binder is added for the purpose of improving the moldability duringmolding and preventing the oxidation of the powder. The binder is notparticularly limited, and heretofore known binders can be used; examplesof the binder may include paraffin. The addition amount of the binder isnot particularly limited, but is preferably 3 to 6 parts by weight inrelation to 100 parts by weight of the raw material powder. The organicsolvent is not particularly limited, but low-boiling-point solvents suchas acetone can be used. The pulverization-mixing time is notparticularly limited; it may be recommended to select the conditionssuch that the average particle size of the hard phase particles formedin the obtained cast material is within the above range; thepulverization-mixing time is usually 15 to 30 hours.

Then, the above-described raw material powder is fused into a fusedmixture, and subsequently, the removal of impurities such as gases andoxides is performed, if necessary. The fusing temperature in this casecan be determined according to the raw materials used, and is preferably1100 to 1300° C., and more preferably 1200 to 1250° C.

Successively, the thus obtained fused mixture is poured into a castingmold such as a mold according to the desired shape and then cooled forcasting, and consequently the cast material can be obtained.

In the present invention, when the fused mixture is cooled, there isincluded a process of continuously cooling the fused mixture at acooling rate of 100° C./min or more, in the temperature range from thecooling starting temperature to 400° C. In the present invention, theinclusion of the process of continuously cooling the fused mixture at acooling rate of 100° C./min or more means that there can be adopted amode in which the cooling rate is 100° C./min or more over a certaincontinuous period; there can be included a process of continuouslycooling at a cooling rate of 100° C./min or more over a period time ofpreferably 1 minute or more and more preferably 5 minutes or more; thereis not included, for example, a mode in which the cooling rate isinstantaneously 100° C./min or more (such as a mode in which the coolingrate is 100° C./min or more, for example, only for 1 second or less).When the fused mixture is cooled, there can be included a process ofcontinuously cooling the fused mixture at a cooling rate of 100° C./minor more in the temperature range from the cooling starting temperatureto 400° C.; the cooling rate in this case is preferably 200° C./min ormore and more preferably 400° C./min or more. By performing the coolingof the fused mixture under the above-described conditions, for theobtained cast material, the average particle size of the hard phaseparticles, the average value of the aspect ratios of the hard phaseparticles, the average value of the major axes of the hard phaseparticles, and the contact ratio between the hard phase particles can becontrolled within the above ranges.

In the present invention, examples of the method for cooling the fusedmixture under the above-described conditions may include, but are notlimited to, a method in which the fused mixture is cooled by pouring thefused mixture into a mold preferably at room temperature to 1100° C.,and more preferably at 300 to 1100° C. As room temperature, thetemperatures of 1 to 30° C. may be quoted.

The cast method is not particularly limited, but it is preferred to use,for example, a mold cast method, a lost-wax cast method, a continuouscast method, a centrifugal cast method, from the viewpoint of beingcapable of forming a cast material having a complicated shape or fromthe viewpoint of being capable of a forming a thick-walled castmaterial.

In such a manner as described above, the cast material according to thepresent invention is manufactured.

The cast material according to the present invention comprises the hardphase particles mainly composed of a boride and/or a carbide, and thebinder phase including an alloy mainly composed of Co and/or Ni, whereinthe average particle size of the hard phase particles is controlled tobe 3 μm or less, the average value of the aspect ratios of the hardphase particles is controlled to be 2.3 or less, the content of the hardphase particles having a major axis exceeding 5 μm is controlled to be 3particles or less per 2,450 μm², and the contact ratio between the hardphase particles is controlled to be 40% or less. Therefore, the castmaterial according to the present invention is excellent in corrosionresistance and wear resistance, and achieves a high hardness and a highbending strength.

Since the cast material according to the present invention is excellentin corrosion resistance and wear resistance, and achieves a highhardness and a high bending strength, the cast material according to thepresent invention can be suitably used as wear resistant materialscapable of achieving an excellent durability even in the environments inwhich high loads are applied, namely, in rolls, cylinders, bearings,industrial pump components and the like.

EXAMPLES

Hereinafter, the present invention will be more specifically describedwith reference to examples, but the present invention is not limited tothese examples.

The definitions of the properties and the evaluation methods of theproperties are as follows.

<Average Particle Size of Hard Phase Particles, Average Value of AspectRatios of Hard Phase Particles, Number of Hard Phase Particles HavingMajor Axis Exceeding 5 μm, and Contact Ratio Between Hard PhaseParticles>

By using a scanning electron microscope (SEM), the backscatteredelectron image of the cross section of the cast material was taken, andaccording to the above-described methods, the average particle size ofthe hard phase particles, the average value of the aspect ratios of thehard phase particles, the number of the hard phase particles having amajor axis exceeding 5 μm, and the contact ratio between the hard phaseparticles were measured. In the present examples, when the respectivemeasurements were performed, the length of the straight-line segment Lwas set at 42 μm and the measurement region range S was set at 2,450μm².

<Hardness>

For the cast material, the measurement of the hardness (Rockwell Cscale) was performed.

<Bending Strength>

A test piece was obtained by cutting the cast material so as to be asize of 4 mm×7 mm×24 mm, and the bending strength (three-point bendingtest) of the obtained test piece was performed according to CIS 026.

Example 1

A mixed powder was obtained by dry mixing 20 wt % of a Mo₂NiB₂-typecomposite boride and, 80 wt % of a Ni-based self-fluxing alloy(composition: Cr: 10 wt %, B: 2 wt %, Si: 2.7 wt %, C: 0.4 wt %, Fe: 2wt %, Ni: the balance). Next, the obtained mixed powder was placed in acrucible, and fused by using a vacuum casting machine (TCP-5250,manufactured by Tanabe Kenden Co., Ltd.) and by raising the temperatureto 1200° C. in a high-frequency fusion furnace to obtain a fusedmixture; the obtained fused mixture at 1200° C. was poured into a moldheated to 400° C., and thereafter air cooled to room temperature toobtain a cast material. In this case, the temperature of the fusedmixture was measured after 2 minutes from the taking out of the fusedmixture from the high-frequency fusion furnace and the temperature wasfound to be 400° C. In other words, the fused mixture was cooled from1200° C. to 400° C. in 2 minutes after being taken out from thehigh-frequency fusion furnace; in this case, the cooling rate of thefused mixture was 400° C./min; from this results, it can be said thatthe fused mixture was continuously cooled at a cooling rate ofapproximately 400° C./min in the range from 1200° C. to 400° C.

Subsequently, for the obtained cast material, according to theabove-described methods, the average particle size of the hard phaseparticles, the average value of the aspect ratios of the hard phaseparticles, the number of the hard phase particles having a major axisexceeding 5 μm, the contact ratio between the hard phase particles, thehardness, and the bending strength were measured. The backscatteredelectron images taken by a scanning electron microscope (SEM) for therespective measurements are shown in FIG. 2(A) and FIG. 2(B). Here, FIG.2(B) is an enlarged image obtained by enlarging a portion of FIG. 2(A).In the backscattered electron images of FIG. 2(A) and FIG. 2(B), thewhite regions are made of a boride (hard phase particle), the blackregions are made of carbides, and the rest gray region is made of aNi-based alloy.

The results of the respective measurements in Example 1 were as follows:the average particle size of the hard phase particles was 2.2 μm, theaverage value of the aspect ratios of the hard phase particles was 2.0,the contact ratio between the hard phase particles was 37%, the hardness(HRC) was 54.8, and the bending strength was 1143 MPa. For the arbitrary10 particles extracted from the hard phase particles used in thecalculation of the aspect ratio, the measured values of the major axisas examples were 2.4 μm, 3.0 μm, 3.5 μm, 3.8 μm, 3.9 μm, 3.9 μm, 4.0 μm,4.4 μm, 4.9 μm, and 5.1 μm; and the average value of the major axis asthe average value of these was 3.89 μm. For all the hard phase particlespresent within measurement region range S (namely, the range of 2,450μm²), the major axes were measured, and the number of the particleshaving a major axis exceeding 5 μm was 1. The measurement of the numberof the particles having a major axis exceeding 5 μm was performed forfive measurement ranges while the measurement range was being altered;in any one of the measurement ranges, the number of the particles havinga major axis exceeding 5 μm was 0 to 1. Alternatively, when for all thehard phase particles present within a range of 5,000 μm², the major axeswere measured, and the number of the particles having a major axisexceeding 5 μm was 2.

Example 2

A mixed powder was obtained by dry mixing 10 wt % of a Mo₂NiB₂-typecomposite boride and, 90 wt % of a Ni-based self-fluxing alloy(composition: B: 2.3 wt %, Si: 7.1 wt %, C: 0.06 wt % or less, Fe: 1.5wt %, Ni: the balance). Next, an ingot was obtained by sintering invacuum the obtained mixed powder by using a vacuum furnace under theconditions of 1160° C. and 30 minutes. Then, a fused mixture wasobtained by raising the temperature of the ingot in the air to 1200° C.to fuse the ingot by using an air atmospheric furnace, and the obtainedfused mixture at 1200° C. was poured into a mold at room temperature of20° C. and subsequently air cooled to obtain a cast material. In thiscase, the temperature of the fused mixture was measured afterapproximately 1 minute from the taking out of the fused mixture from theair atmospheric furnace and the temperature was found to be 400 to 500°C. In other words, the fused mixture was cooled from 1200° C. to 400 to500° C. in 1 minute after being taken out from the air atmosphericfurnace; in this case, the cooling rate of the fused mixture was 700 to800° C./min; from this result, it can be said that the fused mixturepassed through a process of being continuously cooled at a cooling rateof approximately 700 to 800° C./min in the range from 1200° C. to 400°C.

Subsequently, for the obtained cast material, according to theabove-described methods, the average particle size of the hard phaseparticles, the average value of the aspect ratios of the hard phaseparticles, the number of the hard phase particles having a major axisexceeding 5 μm, the contact ratio between the hard phase particles, thehardness, and the bending strength were measured. The backscatteredelectron images taken by a scanning electron microscope (SEM) for therespective measurements are shown in FIG. 3(A) and FIG. 3(B). Here, FIG.3(B) is an enlarged image obtained by enlarging a portion of FIG. 3(A).In the backscattered electron images of FIG. 3(A) and FIG. 3(B), thewhite regions are made of a boride (hard phase particle), the blackregions are made of impurities, and the rest gray region is made of aNi-based alloy.

The results of the respective measurements in Example 2 were as follows:the average particle size of the hard phase particles was 2.8 μm, theaverage value of the aspect ratios of the hard phase particles was 1.5,the contact ratio between the hard phase particles was 14%, the hardness(HRC) was 64, and the bending strength was 1101 MPa. For the arbitrary10 particles extracted from the hard phase particles used in thecalculation of the aspect ratio, the measured values of the major axisas examples were 2.8 μm, 3.8 μm, 2.7 μm, 3.6 μm, 2.8 μm, 2.4 μm, 3.2 μm,3.7 μm, 4.2 μm, and 2.9 μm; and the average value of the major axis asthe average value of these was 3.20 μm. For all the hard phase particlespresent within measurement region range S (namely, the range of 2,450μm²), the major axes were measured, and the number of the particleshaving a major axis exceeding 5 μm was 2. The measurement of the numberof the particles having a major axis exceeding 5 μm was performed forfive measurement ranges while the measurement range was being altered;in any one of the measurement ranges, the number of the particles havinga major axis exceeding 5 μm was 0 to 2. Alternatively, when for all thehard phase particles present within a range of 5,000 μm², the major axeswere measured, and the number of the particles having a major axisexceeding 5 μm was 4.

Example 3

A cast material was obtained in the same manner as in Example 2 exceptthat there was used a mixed powder prepared by dry mixing 15 wt % of aMo₂NiB₂-type composite boride and 85 wt % of a Ni-based self-fluxingalloy (composition: B: 2.3 wt %, Si: 7.1 wt %, C: 0.06 wt % or less, Fe:1.5 wt %, Ni: the balance), and the respective measurements wereperformed in the same manner as in Example 2. The backscattered electronimages taken by a scanning electron microscope (SEM) for the respectivemeasurements are shown in FIG. 4(A) and FIG. 4(B). Here, FIG. 4(B) is anenlarged image obtained by enlarging a portion of FIG. 4(A). In thebackscattered electron images of FIG. 4(A) and FIG. 4(B), the whiteregions are made of a boride (hard phase particle), the black regionsare made of impurities, and the rest gray region is made of a Ni-basedalloy. In the gray region, the elongate shape portion (in FIG. 4(B), theportion indicated by an arrow) is shown in deeper color due to thedifference in crystalloid in the Ni-based alloy, than the other portionof the Ni-based alloy, is still the Ni-based alloy, and is considerednot to constitute the hard phase particles.

The results of the respective measurements in Example 3 were as follows:the average particle size of the hard phase particles was 2.1 μm, theaverage value of the aspect ratios of the hard phase particles was 1.8,the contact ratio between the hard phase particles was 13%, the hardness(HRC) was 65, and the bending strength was 993 MPa. For the arbitrary 10particles extracted from the hard phase particles used in thecalculation of the aspect ratio, the measured values of the major axisas examples were 2.2 μm, 3.1 μM, 3.2 μm, 3.2 μM, 2.6 μm, 4.3 μm, 3.7 μm,3.7 μm, 2.8 μm, and 3.2 μm; and the average value of the major axis asthe average value of these was 3.20 μm. For all the hard phase particlespresent within measurement region range S (namely, the range of 2,450μm²), the major axes were measured, and the number of the particleshaving a major axis exceeding 5 μm was 0. The measurement of the numberof the particles having a major axis exceeding 5 μm was performed forfive measurement ranges while the measurement range was being altered;in any one of the measurement ranges, the number of the particles havinga major axis exceeding 5 μm was 0 to 1. Alternatively, when for all thehard phase particles present within a range of 5,000 μm², the major axeswere measured, and the number of the particles having a major axisexceeding 5 μm was 2.

Example 4

A cast material was obtained in the same manner as in Example 2 exceptthat there was used a mixed powder prepared by dry mixing 20 wt % of aMo₂NiB₂-type composite boride and 80 wt % of a Ni-based self-fluxingalloy (composition: B: 2.3 wt %, Si: 7.1 wt %, C: 0.06 wt % or less, Fe:1.5 wt %, Ni: the balance), and the respective measurements wereperformed in the same manner as in Example 2. The backscattered electronimages taken by a scanning electron microscope (SEM) for the respectivemeasurements are shown in FIG. 5(A) and FIG. 5(B). Here, FIG. 5(B) is anenlarged image obtained by enlarging a portion of FIG. 5(A). In thebackscattered electron images of FIG. 5(A) and FIG. 5(B), the whiteregions are made of a boride (hard phase particle), the black regionsare made of impurities, and the rest gray region is made of a Ni-basedalloy. In the gray region, the elongate shape portion (in FIG. 5(B), theportion indicated by an arrow) is shown in deeper color due to thedifference in crystalloid in the Ni-based alloy, than the other portionof the Ni-based alloy, is still the Ni-based alloy, and is considerednot to constitute the hard phase particles.

The results of the respective measurements in Example 4 were as follows:the average particle size of the hard phase particles was 2.1 μm, theaverage value of the aspect ratios of the hard phase particles was 1.8,the contact ratio between the hard phase particles was 13%, the hardness(HRC) was 65, and the bending strength was 1198 MPa. For the arbitrary10 particles extracted from the hard phase particles used in thecalculation of the aspect ratio, the measured values of the major axisas examples were 3.2 μm, 4.0 μm, 3.4 μm, 3.2 μm, 3.2 μm, 3.7 μm, 3.2 μm,3.0 μm, 3.2 μm, and 3.2 μm; and the average value of the major axis asthe average value of these was 3.31 μm. For all the hard phase particlespresent within measurement region range S (namely, the range of 2,450μm²), the major axes were measured, and the number of the particleshaving a major axis exceeding 5 μm was 2. The measurement of the numberof the particles having a major axis exceeding 5 μm was performed forfive measurement ranges while the measurement range was being altered;in any one of the measurement ranges, the number of the particles havinga major axis exceeding 5 μm was 0 to 2. Alternatively, when for all thehard phase particles present within a range of 5,000 μm², the major axeswere measured, and the number of the particles having a major axisexceeding 5 μm was 4.

Example 5

A cast material was obtained in the same manner as in Example 2 exceptthat only a Ni-based self-fluxing alloy (composition: Cr: 10 wt %, B: 2wt %, Si: 2.7 wt %, C: 0.4 wt %, Fe: 2 wt %, Ni: the balance) was usedin place of a mixed powder, and the respective measurements wereperformed in the same manner as in Example 2. The backscattered electronimages taken by a scanning electron microscope (SEM) for the respectivemeasurements are shown in FIG. 6(A) and FIG. 6(B). Here, FIG. 6(B) is anenlarged image obtained by enlarging a portion of FIG. 6(A). In thebackscattered electron images of FIG. 6(A) and FIG. 6(B), the blackregions are made of a carbide (hard phase particle), and the rest grayregion is made of a Ni-based alloy. It is to be noted that the carbideis probably formed by the reaction of the carbon in the Ni-basedself-fluxing alloy with a metal element (Ni, Cr or Fe).

The results of the respective measurements in Example 5 were as follows:the average particle size of the hard phase particles was 1.1 μm, theaverage value of the aspect ratios of the hard phase particles was 2.4,the contact ratio between the hard phase particles was 18.7%, thehardness (HRC) was 44.7, and the bending strength was 1118 MPa. For thearbitrary 10 particles extracted from the hard phase particles used inthe calculation of the aspect ratio, the measured values of the majoraxis as examples were 1.5 μm, 2 μm, 1.5 μm, 4.5 μm, 4 μm, 2 μm, 2 μm,1.75 μm, 2 μm, and 2 μm; and the average value of the major axis as theaverage value of these was 2.4 μm. For all the hard phase particlespresent within measurement region range S (namely, the range of 2,450μm²), the major axes were measured, and the number of the particleshaving a major axis exceeding 5 μm was 0. The measurement of the numberof the particles having a major axis exceeding 5 μm was performed forfive measurement ranges while the measurement range was being altered;in any one of the measurement ranges, the number of the particles havinga major axis exceeding 5 μm was 0 to 1. Alternatively, when for all thehard phase particles present within a range of 5,000 μm², the major axeswere measured, and the number of the particles having a major axisexceeding 5 μm was 1.

Comparative Example 1

A cast material was obtained as follows: a mixed powder obtained in thesame manner as in Example 1 was placed in a crucible, the temperature ofthe mixed powder was raised to 1200° C. by using a vacuum heat treatmentfurnace (PVSGgr 20/20, manufactured by SHIMADZU CORPORATION) to fuse themixed powder and thus a fused mixture was obtained, the fused mixturewas slowly cooled to 400° C., over approximately 1 hour in ahigh-frequency fusion furnace, and thus a cast material was obtained.Next, for the obtained cast material, the respective measurements wereperformed in the same manner as in Example 1. The backscattered electronimages taken by a scanning electron microscope (SEM) for the respectivemeasurements are shown in FIG. 7(A) and FIG. 7(B). Here, FIG. 7(B) is anenlarged image obtained by enlarging a portion of FIG. 7(A). In thebackscattered electron images of FIG. 7(A) and FIG. 7(B), the whiteregions are made of a boride (hard phase particle), the black regionsare made of a carbide, and the rest gray region is made of a Ni-basedalloy.

The results of the respective measurements in Comparative Example 1 wereas follows: the average particle size of the hard phase particles was3.5 μm, the average value of the aspect ratios of the hard phaseparticles was 2.4, the contact ratio between the hard phase particleswas 43%, the hardness (HRC) was 49.4, and the bending strength was 664MPa. For the arbitrary 10 particles extracted from the hard phaseparticles used in the calculation of the aspect ratio, the measuredvalues of the major axis as examples were 3.4 μm, 3.6 μm, 4.1 μm, 4.2μm, 4.7 μm, 5.1 μm, 5.1 μm, 5.1 μm, 5.6 μm, and 6.4 μm; and the averagevalue of the major axis as the average value of these was 4.73 μm. Forall the hard phase particles present within measurement region range S(namely, the range of 2,450 μm²), the major axes were measured, and thenumber of the particles having a major axis exceeding 5 μm was 5.Alternatively, when for all the hard phase particles present within arange of 5,000 μm², the major axes were measured, and the number of theparticles having a major axis exceeding 5 μm was 10.

Comparative Example 2

A cast material was obtained as follows: a mixed powder obtained in thesame manner as in Example 1 was placed in a crucible, the temperature ofthe mixed powder was raised to 1200° C. by using a vacuum heat treatmentfurnace (PVSGgr 20/20, manufactured by SHIMADZU CORPORATION) to fuse themixed powder and thus a fused mixture was obtained, the fused mixturewas slowly cooled to 800° C., over approximately 5 hours in ahigh-frequency fusion furnace, and thus a cast material was obtained.Next, for the obtained cast material, the respective measurements wereperformed in the same manner as in Example 1. The backscattered electronimages taken by a scanning electron microscope (SEM) for the respectivemeasurements are shown in FIG. 8(A) and FIG. 8(B). Here, FIG. 8(B) is ahigher magnification electron image of the same test piece as for FIG.8(A). In the backscattered electron images of FIG. 8(A) and FIG. 8(B),the white regions are made of a boride (hard phase particle), the blackregions are made of a carbide, and the rest gray region is made of aNi-based alloy.

The results of the respective measurements in Comparative Example 2 wereas follows: the average particle size of the hard phase particles was3.68 μm, the average value of the aspect ratios of the hard phaseparticles was 1.7, the contact ratio between the hard phase particleswas 21%, the hardness (HRC) was 47.0, and the bending strength was 522MPa. For the arbitrary 10 particles extracted from the hard phaseparticles used in the calculation of the aspect ratio, the measuredvalues of the major axis as examples were 3.5 μm, 6 μm, 4 μm, 6 μm, 7.5μm, 8.5 μm, 9.5 μm, 8.5 μm, 6.5 μm, and 5.5 μm; and the average value ofthe major axis as the average value of these was 6.6 μm. For all thehard phase particles present within measurement region range S (namely,the range of 2,450 μm²), the major axes were measured, and the number ofthe particles having a major axis exceeding 5 μm was 10. Alternatively,when for all the hard phase particles present within a range of 5,000μm², the major axes were measured, and the number of the particleshaving a major axis exceeding 5 μm was 20.

Comparative Example 3

A cast material was obtained in the same manner as in ComparativeExample 2 except that only a Ni-based self-fluxing alloy (composition:Cr: 10 wt %, B: 2 wt %, Si: 2.7 wt %, C: 0.4 wt %, Fe: 2 wt %, Ni: thebalance) was used in place of a mixed powder, and the respectivemeasurements were performed in the same manner as in Comparative Example2 The backscattered electron images taken by a scanning electronmicroscope (SEM) for the respective measurements are shown in FIG. 9(A)and FIG. 9(B). Here, FIG. 9(B) is an enlarged image obtained byenlarging a portion of FIG. 9(A). In the backscattered electron imagesof FIG. 9(A) and FIG. 9(B), the black regions are made of a carbide(hard phase particle), and the rest gray region is made of a Ni-basedalloy.

In Comparative Example 3, the hard phase particles were mutually bondedto form large agglomerates, and accordingly, the average particle size,the average value of the aspect ratios and the contact ratio of the hardphase particles were not able to be measured. In the cast material ofComparative Example 3, the hardness (HRC) was 38.0, and the bendingstrength was 519 MPa.

Form the measurement results of Examples 1 to 5, the following castmaterial was shown to be high in bending strength and hardness: acasting material having an average particle size of the hard phaseparticles of 3 μm or less, an average value of the aspect ratios of thehard phase particles of 2.3 or less, a content of the hard phaseparticles having a major axis exceeding 5 μm of 3 particles or less per2,450 μm² and a contact ratio between the hard phase particles of 40% orless. In other words, from the results of Examples 1 to 5, the castmaterials are shown to be cast materials provided with an excellentcorrosion resistance and an excellent resistance, and additionally, ahigh bending strength and a high hardness, namely, the propertiespossessed by a cast material comprising hard phase particles mainlycomposed of a boride and/or a carbide, and a binder phase including analloy mainly composed of Co and/or Ni.

In above-described Examples 2 to 5, the cast materials were obtained bypouring a fused mixture into a mold at room temperature and subsequentlyair-cooling the fused mixture; however, even in a case where a moldheated to 400° C. was used as a mold in the same manner as in Example 1,the fused mixture is regarded to pass through a process of continuouslycooling the fused mixture at a cooling rate of 100° C./min or more, inthe temperature range from the cooling starting temperature to 400° C.;accordingly, the obtained cast material is considered to be a castmaterial similarly having, in addition to an excellent corrosionresistance and an excellent wear resistance, properties being high inbending strength and hardness.

On the other hand, from the results of Comparative Examples 1 and 2, thefollowing cast materials were shown to be low in bending strength: thecast materials having an average particle size of the hard phaseparticles exceeding 3 μm, an average value of the aspect ratios of thehard phase particles exceeding 2.3, a content of the hard phaseparticles having a major axis exceeding 5 μm is 3 particles per 2,450μm², and a contact ratio between the hard phase particles exceeding 40%major axis.

From the measurement results of Comparative Example 3, a cast materialin which the hard phase particles were mutually bonded to form largeagglomerates was shown to be low both in bending strength and inhardness.

1. A cast material comprising hard phase particles mainly composed of a boride and/or a carbide and a binder phase including an alloy mainly composed of Co and/or Ni, wherein the average particle size of the hard phase particles is 3 μm or less, the average value of the aspect ratios of the hard phase particles is 2.3 or less, the content of the hard phase particles having a major axis exceeding 5 μm is 3 particles or less per 2,450 μM², and the contact ratio between hard phase particles is 40% or less.
 2. The cast material according to claim 1, wherein: the hard phase particles are the boride and/or the carbide comprising at least one of Ni, Co, Cr, Mo, Mn, Cu, W, Fe and Si, and B and/or C.
 3. The cast material according to claim 1, wherein: the binder phase is the alloy comprising at least one of Cr, Mo, Mn, Cu, W, Fe and Si, and Co and/or Ni.
 4. The cast material according to claim 1, wherein: the content of B in the cast material is 1 to 6 wt % and the content of C in the cast material is 0 to 2.5 wt %.
 5. The cast material according to claim 1, wherein: the hard phase particles comprise a composite boride represented by Mo₂NiB₂ or Mo₂(Ni,Cr)B₂, and the binder phase comprises a Ni-based alloy.
 6. A method of manufacturing a cast material comprising hard phase particles mainly composed of a boride and/or a carbide, and a binder phase including an alloy mainly composed of Co and/or Ni, comprising: obtaining a fused mixture by fusing the raw materials, for forming the cast material in a state of being mixed with each other, and cooling the fused mixture, wherein the cooling of the fused mixture includes a process of continuously cooling the fused mixture, at a cooling rate of 100° C./min or more, in a temperature range from the cooling starting temperature to 400° C.
 7. The method of manufacturing a cast material according to claim 6, wherein: the cooling of the fused mixture is performed by pouring the fused mixture into a mold set at room temperature to 1100° C. 